The Age of Questions: Or, A First Attempt at an Aggregate History of the Eastern, Social, Woman, American, Jewish, Polish, Bullion, Tuberculosis, and Many Other Questions over the Nineteenth Century, and Beyond (Princeton, N.J.: Princeton University Press, 2018).

Between States: The Transylvanian Question and the European Idea during World War II (Stanford, Calif.: Stanford University Press, 2009).

“The Quiet Revolution: Consuls and the International System in the Nineteenth Century,” in The Balkans as Europe, 1821-1914, Timothy Snyder and Katherine Younger, eds. (Rochester, NY: University of Rochester Press, 2018), pp. 110-138.